Interpretive Summary: The development of high yielding cultivars is essential to sustain economic cotton production. Tobacco budworms are serious pests of cotton in the mid-South production area. Information is limited on the level of resistance of cultivars to the tobacco budworm. The objective of this study was to evaluate cotton cultivar performance when tobacco budworms were present in high numbers. Cotton cultivars were evaluated from 1988-1992 in field tests using two treatments. Treatment one was a high level of tobacco budworms which was obtained by artificially applying first instar larvae beginning at first square for four to six weeks. Treatment two was a low level of tobacco budworms which was achieved by weekly applications of insecticides. Lint yield produced in the two treatments was the criteria used for evaluation. Yields were significantly reduced, across all years, when cultivars were grown under high levels of tobacco budworms. The yields in the high treatment ranged from 40 to 60% of those in the low treatment. Only moderate levels of resistance to the tobacco budworm were detected. Even though breeders have developed high yielding cultivars, progress is still needed in the development of resistance to the tobacco budworm.

Technical Abstract:
The development of cotton Gossypium hirsutum L. cultivars is essential for economic production. Information is limited on how cotton cultivars perform under elevated levels of tobacco budworm, Heliothis virescens (F.), an economic cotton pest. Seven field tests were conducted between 1988 and 1992 to evaluate cotton cultivars when grown under elevated levels of tobacco budworms. Cultivars were grown under two regimes: (1) artificial infestation, w/TBW and (2) control of insect pests, w/o TBW. Elevated levels of TBW (w/TBW) significantly reduced yields which varied among years and tests. The regression equation for lint yield w/TBW on lint yield w/o TBW was Y = -100.7 + 0.6 X, with an r2 of 0.57. Thus, for every 1.00 lb of lint yield increase due to cultivar improvement there was a corresponding increase under TBW infestation of only 0.6 lb. The regression coefficient for lint percentage on lint yield w/o TBW was significant (Y = 30.85 + 0.006 X, R2 0.44). These data show that cotton breeders have developed high yielding cultivars; however, progress is still needed in the development of resistance to the tobacco budworm. They also show that as cultivars with higher yield are developed the same cultivars are better able to withstand damage by the tobacco budworm. The parity between yield increase per se and yield under elevated levels of tobacco budworm is not 1.0:1:0 but rather 1.0:0.6. This is a useful and practical level of parity.